The present invention relates to the general field of methods of fabricating needled fiber structures suitable for being used in fabricating parts made of composite material.
Various types of needling machine are known that are suitable for making needled textile structures. In a first machine of plane type, fiber layers that are stacked on a table are needled, with the table moving horizontally in translation past the needling head, which is movable vertically. In a second machine of circular type, a continuous fiber layer that is wound around a rotary mandrel is needled. The mandrel presents a surface of revolution having the layer wound around it, with the layer being situated facing a needling head that is movable in a direction perpendicular to that surface.
When using one or the other of those machines for needling a plurality of superposed fiber layers, it is found that the resulting needled fiber structures present zones of weakness. These zones of weakness are due in particular to recurrent needling on the same zone for two consecutive fiber layers. In particular, when the needling head moves along the fiber layer for needling (e.g. as a result of the table moving in translation or of the mandrel rotating), successive passes of the head for two layers can produce holes that are in alignment in the travel direction of the layer (a phenomenon referred to as “lining”). Such alignment of holes within a given layer and for different layers can lead to premature breaking of the needled fiber structure along those lines of holes. Thereafter, it is found that parts made of composite material by densifying such needled fiber structures also suffer from mechanical strength problems, which is not desirable.
There therefore exists a need for a method of fabricating a needled textile structure on a needling machine of a plane or circular type that does not present the above-mentioned drawbacks.